MEMS semiconductor devices are increasingly finding applications in optical (MOEMS) and other applications where one or more surfaces are used as reflectors or for other purposes requiring a planar surface on an outer element of the finished micromachined product.
The typical micromachined structure results from many processes of diffusion, layer growth and stripping, oxidation, and metalization to name a few. These steps are often performed at different elevated temperatures. The result is the creation of a distribution of stresses throughout the MEMS device. The stresses vary from compressive to tensile stresses and produce a complex pattern of deflection forces through the semiconductor structure.
Where these devices include a lamella this is freed from the body of the semiconductor in the final stages of production, these deflection forces are free to deform the lamella into a curved shape that impairs the effectiveness of the lamella as a reflector or other element dependent on a planar outer surface.